Skipped wells and scientific error during fosfomycin agar dilution and broth microdilution lead to inconsistent minimal inhibitory concentrations and may be cause for reevaluating testing methods for Klebsiella pneumoniae.

Despite the first-line recommendation of fosfomycin for uncomplicated urinary tract infections (UTIs), there are pressing barriers for optimizing its use for the treatment of non-Escherichia coli Enterobacterales UTI. There are no approved breakpoints for oral use against other Enterobacterales, and the recommended agar dilution (AD) reference method for minimal inhibitory concentration (MIC) determination is largely impractical. Using 160 clinical Klebsiella pneumoniae isolates, we sought to understand rates of skipped wells and MIC imprecision in broth microdilution (BMD) and how that compares to rates of error using AD. Though the Clinical and Laboratory Standards Institute refers to the skipped well phenomena in their recommendation against the use of BMD, there is a paucity of data on its frequency. While AD and BMD produced similar MIC50/90 values (32/256 µg/mL for AD and 64/256 µg/mL for BMD), essential agreement was poor. No-growth wells at concentrations below the MIC occurred in up to 10.9% of wells at a given concentration, as the most frequent scientific error. Growth in concentrations above the measured MIC occurred in up to 3.3% of wells and was seen within three dilutions of the MIC for BMD. Observation of single colonies either at or beyond the measured MIC for AD was also common and occurred up to 8.3% and 2.5% of the time, respectively. The frequent scientific error in both testing methods should prompt re-evaluation of AD guidelines and expansion of MIC testing methods for fosfomycin susceptibility testing, as poor agreement with another method prone to scientific error should not be the main detractor from BMD use.IMPORTANCEDespite the recommendation of fosfomycin for uncomplicated urinary tract infections (UTIs), there are barriers for optimizing its use. There are no approved breakpoints for oral use against other Enterobacterales, and the recommended agar dilution (AD) reference method for MIC determination is largely impractical. The use of broth microdilution (BMD) for fosfomycin testing is not recommended by the Clinical and Laboratory Standards Institute due to unsatisfactory precision and skipped wells-occurrence of no-growth in a single well before the minimal inhibitory concentration (MIC)-and trailing endpoints. We sought to understand rates of skipped wells and growth at concentrations above measured MICs in BMD and how that compares to scientific error using AD. No-growth wells at concentrations below the MIC occurred in up to 10.9% of wells for BMD and single colonies at or beyond measured MICs for AD were also common. Frequent scientific error in both methods should prompt re-evaluation of both AD and BMD for fosfomycin susceptibility testing.

Predictors of adverse safety events and unscheduled care among an outpatient parenteral antimicrobial therapy (OPAT) patient cohort.

Background: Select circumstances require outpatient parenteral antimicrobial therapy (OPAT). The potency of OPAT agents presents an increased risk of adverse events and unscheduled medical care. We analyzed these outcomes among OPAT recipients as part of the implementation of a collaborative OPAT program. Methods: Adult patients discharged home from an academic hospital with OPAT between January 2019 and June 2021 were included in this retrospective cohort; participants discharged between June 2020 and June 2021 were part of the collaborative OPAT program. Patients with cystic fibrosis were excluded. Data on patient characteristics and outcomes were collected from electronic medical records by two reviewers. Multivariable analysis was conducted to identify predictors of vascular access device (VAD) complications, adverse drug events (ADEs), and OPAT-related emergency department (ED) visits and rehospitalizations. Results: Among 265 patients included in the cohort, 57 (21.5%) patients experienced a VAD complication; obesity [odds ratio (OR): 3.32; 95% confidence interval (CI): 1.38-8.73; p = 0.01) and multi-drug therapy (OR: 2.56; 95% CI: 1.21-5.39; p = 0.01) were associated with an increased odds of VAD complication. Eighty-two (30.9%) participants experienced an ADE; 30 (11.3%) experienced a severe/serious ADE. Lipo/glycopeptide receipt, (OR: 5.28; 95% CI: 1.89-15.43; p < 0.01) and Black/African American race (OR: 4.85; 95% (CI): 1.56-15.45; p < 0.01) were associated with an increased odds of severe/serious ADE. Inclusion in the OPAT collaborative was associated with a decreased odds of severe/serious ADE (OR: 0.26; 95% CI: 0.08-0.77; p = 0.01). Fifty-eight (21.9%) patients experienced an OPAT-related ED visit and 53 (20.0%) experienced an OPAT-related rehospitalization. VAD complication (OR: 2.37; 95% (CI): 1.15-4.86, p = 0.02) and ADEs (OR: 2.19; CI: 1.13-4.22; p = 0.02) were associated with OPAT-related ED visits. ADE was associated with 90-day OPAT-related rehospitalization (OR: 3.21; (CI): 1.59-6.58; p < 0.01). Conclusion: Adverse safety events and OPAT-related unscheduled care occurred often in our cohort. A structured OPAT program that includes ID pharmacist antibiotic reconciliation may reduce rates of ADEs.

Academic Activism: An Avenue to Action.

Until now, the term "advocacy" in pharmacy education and practice has focused on advocating for the advancement of the pharmacy profession or patient advocacy. With the 2022 Curricular Outcomes and Entrustable Professional Activities publication, the focus of advocacy has broadened to include advocacy for other causes that impact the health of patients. This commentary will highlight 3 pharmacy-focused organizations advocating for social issues impacting the health of patients as well as encourage members of the Academy to continue to expand personal social advocacy efforts.

Fosfomycin Disk Diffusion Testing among Klebsiella pneumoniae Results in Frequent Inner Colonies and Categorical Disagreement Based on Conflicting Breakpoint Organization Recommendations.

Recent studies indicate that discrete inner colonies (ICs) arise during fosfomycin disk diffusion (DD) testing. CLSI and EUCAST have contradicting recommendations on the interpretation of ICs; CLSI recommends considering them while EUCAST recommends ignoring them when interpreting DD results. We sought to compare the categorical agreement of DD and agar dilution (AD) MIC and to assess the implications of ICs interpretation on zone diameter readings. A convenience sample of 80 Klebsiella pneumoniae clinical isolates with varied phenotypic profiles collected from 3 United States locations was included. Susceptibility was determined in duplicate, using both organization recommendations and interpretations for Enterobacterales. Correlations between methods were calculated using EUCASTIV AD as the reference method. MIC values ranged from 1 to >256 µg/mL with an MIC50/90 of 32/256 µg/mL. Extrapolating EUCASToral and CLSI AD Escherichia coli breakpoints, 12.5% and 83.8% of isolates were susceptible, respectively, whereas 66.3% were susceptible by EUCASTIV AD-which applies to K. pneumoniae. CLSI DD measurements were 2 to 13 mm smaller than EUCAST measurements due to 66 (82.5%) isolates producing discrete ICs. Categorical agreement with EUCASTIV AD was greatest for CLSI AD (65.0%) and poorest for EUCASToral DD (6.3%). Isolates among this collection were frequently classified into different interpretive categories based on varying breakpoint organization recommendations. The more conservative oral breakpoints of EUCAST resulted in more isolates categorized as resistant despite frequent ICs. Differing zone diameter distributions and poor categorical agreement highlight issues of extrapolating E. coli breakpoints and methods to other Enterobacterales, and the clinical relevance of this issue warrants further investigation. IMPORTANCE Fosfomycin susceptibility testing recommendations are complex. Both the Clinical and Laboratory Standards Institute and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) recognize agar dilution as the reference method, but they also support disk diffusion as an approved method for Escherichia coli. However, these two organizations have conflicting recommendations for the interpretation of inner colonies that arise during disk diffusion testing which can lead to varying zone diameters and interpretations despite isolates having identical MIC values. Using a collection of 80 Klebsiella pneumoniae isolates, we found that a large (82.5%) portion produced discrete inner colonies during disk diffusion and isolates were frequently classified into different interpretive categories. The more conservative breakpoints of EUCAST resulted in more isolates categorized as resistant despite frequent inner colonies. Differing zone diameter distributions and poor categorical agreement highlight issues of extrapolating E. coli breakpoints and methods to other Enterobacterales, and the clinical relevance of this issue warrants further investigation.

Antimicrobial susceptibility testing: An updated primer for clinicians in the era of antimicrobial resistance: Insights from the Society of Infectious Diseases Pharmacists.

Antimicrobial susceptibility testing (AST) is a critical function of the clinical microbiology laboratory and is essential for optimizing care of patients with infectious diseases, monitoring antimicrobial resistance (AMR) trends, and informing public health initiatives. Several methods are available for performing AST including broth microdilution, agar dilution, and disk diffusion. Technological advances such as the development of commercial automated susceptibility testing platforms and the advent of rapid diagnostic tests have improved the rapidity, robustness, and clinical application of AST. Numerous accrediting and regulatory agencies are involved in the process of AST and setting and revising breakpoints, including the U.S. Food and Drug Administration and the Clinical and Laboratory Standards Institute. Challenges to optimizing AST include the emergence of new resistance mechanisms, the development of new antimicrobial agents, and generation of new data requiring updates and revisions to established methods and breakpoints. Together, the challenges in AST methods and their interpretation create important opportunities for well-informed clinicians to improve patient outcomes and provide value to antimicrobial stewardship programs, especially in the setting of rapidly changing and increasing AMR. Addressing AST challenges will involve continued development of new technologies along with collaboration between clinicians and the laboratory to facilitate optimal antimicrobial use, combat the increasing burden of AMR, and inform the development of novel antimicrobials. This updated primer serves to reinforce important principles of AST, and to provide guidance on their implementation and optimization.

Prevalence and characteristics of multidrug-resistant Escherichia coli sequence type ST131 at two academic centers in Boston and Minneapolis, USA.

BACKGROUND: Escherichia coli sequence type (ST) ST131, with its emergent resistance-associated H30Rx, H30R1, and C1-M27 clonal subsets, accounts for the greatest share of extraintestinal E. coli infections and most extended-spectrum ß-lactamase (ESBL)-producing E. coli. METHODS: We characterized and compared consecutive E. coli urine isolates from two geographically distinct medical centers in Minneapolis, Minnesota (n = 172) and Boston, Massachusetts (n = 143) for ESBL phenotype, CTX-M-type ESBL genes, phylogenetic groups, selected ST131 subclones, and 40 extraintestinal virulence genes. RESULTS: Whereas the Boston vs. Minneapolis isolates had a similar prevalence of phylogenetic groups (mainly B2: 79% vs 73%), ST131 (34% vs 28%), H30 (28% vs 21%), and H30Rx (6% vs 5%), the emerging C1-M27 subclone occurred uniquely among Boston (6%) isolates. ESBL production was more prevalent among Boston isolates (15% vs 8%) and among ST131 isolates. Identified ESBL genes included blaCTX-M-27 (Boston only) and blaCTX-M-15. Ciprofloxacin resistance was ST131-associated and similarly prevalent across centers. Boston isolates had higher virulence gene scores. CONCLUSIONS: Despite numerous similarities to Minneapolis isolates, Boston ST131 isolates demonstrated more prevalent ESBL production, higher virulence gene scores, and, uniquely, the C1-M27 subclone and blaCTX-M-27. Broader surveillance is needed to define the prevalence of ST131's globally successful C1-M27 subclone across the U.S.

Minnesota One Health Antibiotic Stewardship Collaborative: A Reproducible Approach to Facilitate Antimicrobial Stewardship Progress.

The Minnesota One Health Antibiotic Stewardship Collaborative (MOHASC) was launched in 2016 with the mission of providing a collaborative environment to promote judicious antibiotic use and antibiotic stewardship (AS) and to reduce the impact of antibiotic-resistant pathogens of human, animal, and environmental health importance. MOHASC goals include improving AS programs in healthcare and veterinary medicine, advancing understanding of environmental impacts of antibiotic use, and promoting a One Health (OH) approach to AS. These goals are accomplished through quarterly meetings of 4 work groups, field trips, collaborative research, an annual member meeting, and public education events. This novel OH approach has strengthened multidisciplinary relationships within Minnesota and led to procurement of funding to enhance AS initiatives beyond the Collaborative. This perspective serves as a blueprint for other jurisdictions, and we advocate for use of this reproducible OH strategy to facilitate broad AS goals.

Opportunities for antibiotic stewardship in emergency department or hospitalized patients with asymptomatic bacteriuria: identifying risk factors for antibiotic treatment.

Antibiotic treatment of asymptomatic bacteriuria (ASB) is considered inappropriate and may lead to adverse events. This 2-center, retrospective cohort study including emergency department or inpatient adults identified pyuria (odds ratio, 2.43; 95% confidence interval, 1.17-5.01; P = .02) as the only independent risk factor for antibiotic treatment of ASB.

The antimicrobial peptide DGL13K is active against drug-resistant gram-negative bacteria and sub-inhibitory concentrations stimulate bacterial growth without causing resistance.

Antimicrobial peptides may be alternatives to traditional antibiotics with reduced bacterial resistance. The antimicrobial peptide GL13K was derived from the salivary protein BPIFA2. This study determined the relative activity of the L-and D-enantiomers of GL13K to wild-type and drug-resistant strains of three gram-negative species and against Pseudomonas aeruginosa biofilms. DGL13K displayed in vitro activity against extended-spectrum beta-lactamase (ESBL)-producing and Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae (MICs 16-32 µg/ml), MDR and XDR P. aeruginosa, and XDR Acinetobacter baumannii carrying metallo-beta-lactamases (MICs 8-32 µg/ml). P. aeruginosa showed low inherent resistance to DGL13K and the increased metabolic activity and growth caused by sub-MIC concentrations of GL13K peptides did not result in acquired bacterial resistance. Daily treatment for approximately two weeks did not increase the MIC of DGL13K or cause cross-resistance between LGL13K and DGL13K. These data suggest that DGL13K is a promising antimicrobial peptide candidate for further development.

The Atypical Antipsychotic Quetiapine Promotes Multiple Antibiotic Resistance in Escherichia coli.

Atypical antipsychotic (AAP) medication is a critical tool for treating symptoms of psychiatric disorders. While AAPs primarily target dopamine (D2) and serotonin (5HT2A and 5HT1A) receptors, they also exhibit intrinsic antimicrobial activity as an off-target effect. Because AAPs are often prescribed to patients for many years, a potential risk associated with long-term AAP use is the unintended emergence of bacteria with antimicrobial resistance (AMR). Here, we show that exposure to the AAP quetiapine at estimated gut concentrations promotes AMR in Escherichia coli after 6 weeks. Quetiapine-exposed isolates exhibited an increase in MICs for ampicillin, tetracycline, ceftriaxone, and levofloxacin. By whole-genome sequencing analysis, we identified mutations in genes that confer AMR, including the repressor for the multiple antibiotic resistance mar operon (marR), and real-time reverse transcription-quantitative PCR (RT-qPCR) analysis showed increased levels of marA, acrA, and tolC mRNAs and reduced levels of ompF mRNA in the isolates carrying marR mutations. To determine the contribution of each marR mutation to AMR, we constructed isogenic strains carrying individual mutant marR alleles in the parent background and reevaluated their resistance phenotypes using MIC and RT-qPCR assays. While marR mutations induced robust activity of the mar operon, they resulted in only modest increases in MICs. Interestingly, although these marR mutations did not fully recapitulate the AMR phenotype of the quetiapine-exposed isolates, we show that marR mutations promote growth fitness in the presence of quetiapine. Our findings revealed an important link between the use of AAPs and AMR development in E. coli. IMPORTANCE AAP medication is a cornerstone in the treatment of serious psychiatric disease. The AAPs are known to exhibit antimicrobial activity; therefore, a potential unintended risk of long-term AAP use may be the emergence of AMR, although such risk has received little attention. In this study, we describe the development of multidrug antibiotic resistance in Escherichia coli after 6 weeks of exposure to the AAP quetiapine. Investigation of mutations in the marR gene, which encodes a repressor for the multiple antibiotic resistance (mar) operon, reveals a potential mechanism that increases the fitness of E. coli in the presence of quetiapine. Our findings establish a link between the use of AAPs and AMR development in bacteria.

Brighter horizons: The necessity of concentrated sponsorship targeted toward minoritized student pharmacists.

Due to the effects of structural racism, disproportionately lower numbers of Black, Hispanic or LatinX, American Indian, and Alaska Native students pursue a career in pharmacy and successfully matriculate into the profession. Despite these disparities being present for many years, little progress has been achieved in diversifying the pharmacy profession, resulting in a persistent lack of diversity within pharmacy leadership across employers and pharmacy organizations. Consistent with recent recommendations for improving diversity in pharmacy, the PharmGradWishlist (PGWL) initiative was created as a way for practicing pharmacists and organizations to provide direct financial sponsorship to racially and ethnically minoritized trainees to offset costs incurred during training and during the transition from student to practicing pharmacist. Many of these costs, such as residency and fellowship application fees, job interview travel costs, board exam and licensing fees, and moving expenses, are not typically subsidized by federal student funding. Offsetting these costs is an important way to reduce barriers to entering the profession and postgraduate training, the latter of which may be particularly important in trainees' pursuit of academic and leadership positions in pharmacy. The initial development and advertisement of the initiative occurred through social media and the grassroots efforts of the PGWL team, a group of 10 volunteer pharmacists from across the country, and resulted in generous donations from a small proportion of practicing pharmacists nationwide. It is now time for the profession as a whole to embrace the role of direct sponsorship in improving diversity in the profession. We call upon pharmacists and pharmacy organizations to advocate for and participate in financial sponsorship of racially and ethnically minoritized trainees and pharmacists as a way to increase diversity and promote health equity.

In a Pinch: Cefiderocol for CRAB Infections.

Carbapenem-resistant Acinetobacter baumannii (CRAB) can cause significant infections with limited treatment options available. Falcone et al. (https://doi.org/10.1128/aac.02142-21) describe a single-center retrospective study comparing clinical outcomes among patients with CRAB infections treated with cefiderocol-containing versus colistin-containing regimens. Patients who received cefiderocol-containing regimens had lower 30-day mortality, though there are several limitations raised here, which make interpretation and applicability difficult.

Differences in Fosfomycin Resistance Mechanisms between Pseudomonas aeruginosa and Enterobacterales.

Multidrug-resistant (MDR) Pseudomonas aeruginosa presents a serious threat to public health due to its widespread resistance to numerous antibiotics. P. aeruginosa commonly causes nosocomial infections including urinary tract infections (UTI) which have become increasingly difficult to treat. The lack of effective therapeutic agents has renewed interest in fosfomycin, an old drug discovered in the 1960s and approved prior to the rigorous standards now required for drug approval. Fosfomycin has a unique structure and mechanism of action, making it a favorable therapeutic alternative for MDR pathogens that are resistant to other classes of antibiotics. The absence of susceptibility breakpoints for fosfomycin against P. aeruginosa limits its clinical use and interpretation due to extrapolation of breakpoints established for Escherichia coli or Enterobacterales without supporting evidence. Furthermore, fosfomycin use and efficacy for treatment of P. aeruginosa are also limited by both inherent and acquired resistance mechanisms. This narrative review provides an update on currently identified mechanisms of resistance to fosfomycin, with a focus on those mediated by P. aeruginosa such as peptidoglycan recycling enzymes, chromosomal Fos enzymes, and transporter mutation. Additional fosfomycin resistance mechanisms exhibited by Enterobacterales, including mutations in transporters and associated regulators, plasmid-mediated Fos enzymes, kinases, and murA modification, are also summarized and contrasted. These data highlight that different fosfomycin resistance mechanisms may be associated with elevated MIC values in P. aeruginosa compared to Enterobacterales, emphasizing that extrapolation of E. coli breakpoints to P. aeruginosa should be avoided.

A Multicenter Evaluation of Ceftolozane/Tazobactam Treatment Outcomes in Immunocompromised Patients With Multidrug-Resistant Pseudomonas aeruginosa Infections.

BACKGROUND: Real-world data assessing outcomes of immunocompromised patients treated with ceftolozane/tazobactam (C/T) are limited. This study evaluated treatment and clinical outcomes of immunocompromised patients receiving C/T for multidrug-resistant (MDR) Pseudomonas aeruginosa. METHODS: This was a 14-center retrospective cohort study of adult immunocompromised inpatients treated for ≥24 hours with C/T for MDR P. aeruginosa infections. Patients were defined as immunocompromised if they had a history of previous solid organ transplant (SOT), disease that increased susceptibility to infection, or received immunosuppressive therapies. The primary outcomes were all-cause 30-day mortality and clinical cure. RESULTS: Sixty-nine patients were included; 84% received immunosuppressive agents, 68% had a history of SOT, and 29% had diseases increasing susceptibility to infection. The mean patient age was 57 ± 14 years, and the median (interquartile range) patient Acute Physiology and Chronic Health Evaluation II and Charlson Comorbidity Index scores were 18 (13) and 5 (4), respectively, with 46% receiving intensive care unit care at C/T initiation. The most frequent infection sources were respiratory (56%) and wound (11%). All-cause 30-day mortality was 19% (n = 13), with clinical cure achieved in 47 (68%) patients. Clinical cure was numerically higher (75% vs 30%) in pneumonia patients who received 3-g pneumonia regimens vs 1.5-g regimens. CONCLUSIONS: Of 69 immunocompromised patients treated with C/T for MDR P. aeruginosa, clinical cure was achieved in 68% and mortality was 19%, consistent with other reports on a cross-section of patient populations. C/T represents a promising agent for treatment of P. aeruginosa resistant to traditional antipseudomonal agents in this high-risk population.

Performance of Four Fosfomycin Susceptibility Testing Methods against an International Collection of Clinical Pseudomonas aeruginosa Isolates.

Fosfomycin has been shown to have a wide spectrum of activity against multidrug-resistant Gram-negative bacteria; however, breakpoints have been established only for Escherichia coli or Enterobacterales per the Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST), respectively. A lack of additional organism breakpoints limits clinical use of this agent and has prompted extrapolation of these interpretive categories to other organisms like Pseudomonas aeruginosa without supporting evidence. Further complicating the utility of fosfomycin is the specified method for MIC determination, namely, agar dilution, which is not widely available and is both labor and time intensive. We therefore sought to determine the susceptibility of a large international collection of P. aeruginosa isolates (n = 198) to fosfomycin and to compare testing agreement rates across four methods: agar dilution, broth microdilution, disk diffusion, and Etest. Results were interpreted according to CLSI E. coli breakpoints, with 49.0 to 85.8% considered susceptible, dependent upon the testing method used. Epidemiological cutoff values were calculated and determined to be 256 µg/ml and 512 µg/ml for agar dilution and broth microdilution, respectively. Agreement rates were analyzed using both agar dilution and broth microdilution with a resulting high essential agreement rate of 91.3% between the two susceptibility testing methods. These results indicate that broth microdilution may be a reliable method for fosfomycin susceptibility testing against P. aeruginosa and stress the need for P. aeruginosa-specific breakpoints.

Ceftolozane-tazobactam and ceftazidime-avibactam activity against ß-lactam-resistant Pseudomonas aeruginosa and extended-spectrum ß-lactamase-producing Enterobacterales clinical isolates from U.S. medical centres.

BACKGROUND: Despite availability of ceftolozane-tazobactam (C/T) and ceftazidime-avibactam (CZA) for several years, the individual spectrum of activity of each agent may not be widely known. We compared the activity of C/T and CZA against convenience samples of 119 extended-spectrum ß-lactamase (ESBL)-producing Enterobacterales and 60 ß-lactam-resistant Pseudomonas aeruginosa clinical isolates collected from three U.S. institutions. METHODS: Minimal inhibitory concentrations (MICs) for C/T and CZA were determined by broth microdilution. Molecular identification of nine ß-lactamase gene targets was conducted for Enterobacterales and P. aeruginosa isolates with increased MICs to C/T or CZA. RESULTS: More than 90% of Enterobacterales isolates demonstrated susceptibility to both C/T and CZA, in contrast to the other traditional ß-lactam agents tested, which were much less active. The MIC50/90 values were nearly equivalent between agents. The most common ß-lactamase genes identified in Enterobacterales isolates with MIC values ≥2 mg/L were the CTX-M-1 group (85%) and CMY-2-like (23%) ß-lactamases. Both agents were active against >80% of ß-lactam-resistant P. aeruginosa isolates tested, most of which had oprD mutations identified. One P. aeruginosa isolate was positive for a Klebsiella pneumoniae carbapenemase-type gene but remained meropenem-susceptible. The MIC50 values were four-fold lower in favour of C/T (1 mg/L vs. 4 mg/L) against P. aeruginosa. CONCLUSIONS: Our data suggest that either agent may be a reasonable choice for centres with a high proportion of ESBL producers; however, C/T may have improved activity against P. aeruginosa and may be preferred in institutions with a higher frequency of resistant pseudomonal isolates.

Assessment of mortality stratified by meropenem minimum inhibitory concentration in patients with Enterobacteriaceae bacteraemia: A patient-level analysis of published data.

In 2010, the Clinical and Laboratory Standards Institute (CLSI) lowered carbapenem breakpoints to reduce the proportion of 'susceptible' organisms that produced carbapenemases. Few studies have evaluated the effect of this change on clinical outcomes. This systematic review aimed to evaluate the effect of carbapenem MICs on 30-day mortality from pooled patient-level data from studies of patients treated with carbapenems across a range of meropenem MICs. PubMed was searched to March 2019 with the terms 'carbapenem', 'meropenem', 'imipenem', 'doripenem', 'ertapenem', 'susceptibility' and 'outcomes'. Studies were included in the analysis if patients had Enterobacteriaceae bacteraemia treated with a carbapenem for ≥48 h and mortality was reported. Studies were excluded if all isolates were either susceptible or resistant to meropenem based on CLSI 2010 breakpoints or if only carbapenemase-producing isolates were included. Authors were contacted for patient-level data. The primary outcome was 30-day mortality, with planned subset analyses of patients treated with meropenem, receiving active combination therapy, treated in the ICU or infected with Klebsiella pneumoniae. Of 157 articles identified, 4 met the inclusion criteria (115 eligible patients). The odds of mortality increased with each increasing meropenem MIC dilution (OR = 1.51, 95% CI 1.06-2.15) as a continuous variable. A similar increase in odds was observed in patients treated with meropenem, treated in the ICU, infected with K. pneumoniae or receiving no other active antimicrobials. Increasing meropenem MICs in Enterobacteriaceae were associated with increased mortality; however, more work is needed to define optimal clinical decision rules for infections within the susceptible range.